Signaling system



Feb. 2l, 1933. Q s DEMAREST 1,898,118

S IGNALING SYSTEM Filed Nov. l0, 1931 gg M@ a We@ INVENTOR Y @.Semowes ATTORNEY Patented Feb. 21, 1933 UNITED STATES PATENT i oFFlcE CHARLES S. DEMABEST, F RIDGEWOOD, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAIH COMPANY, A CORPORATION OF NEW -YORK SIGNALING- SYSTEM Application llled November 10, 1931.

'lhis invention relates to transmission systems and more particularly to improvements in signaling arrangements associated with such systems.

The signaling arrangements of the invention are particularly useful on telephone sys tems. An illustration of a particular type of telephone system on which the arrangements of the invention might be used would l@ be the case Where frequencies Within the voice range are utilized for signaling purposes and in Which it is desired to obtaln several distinctive signals. For example, a .base freduency of 1000 cycles might be utilized for slgnaling and this frequency might be interrupted at different rates, such as l5, 25, 35 and cycles, to give distinctive signals. Reference is had to the above specific system for purposes of illustration onl and the 2@ signaling arrangements of the invention are capable of use with other types of transmission systems.

ln the 1000 cycle toll signaling system W above referred to, it has heretofore been the 2* practice to utilize a two-stage receiving amplier-detector which employs a plurality of high vacuum thermionic tubes. Signaling current of 1000 cycles is used and is interrupted at the rate of :20 cycles per second in 5@ order to give the signal a distinguishing characteristic and so as to aid in avoiding interference from the voice currents and transients The used output of the detector is edectively 20 cycle current. rlhis current operates a sensitive polar relay Which, through its contacts, causes a condenser to 'be alternately charged and discharged through a local direct current relay and an inductance which tunes the circuit to 20 cycles. The local direct current relay would control a local signaling circuit. lln the above type of system an ampliiier is employed ahead of the detector tube because the use A, of three electrode vacuum tubes requires this l in order to obtain sucient power for the Serial No. 574,205.

operation of the polar receiving relay with the low values of signaling current used in practice. A sensitive polar relay is necessary f-or receiving because suflicient energy 1snot received from the' detector to operate directly the types of direct current relays available for use in the local signaling circuits.

ln the arrangements of the invention a gas illed thermionic tube is utilized in place of the separate amplifier and detector tubes of other types of systems. This presents an advantage of economy and improvement in operation. One tube unit will accomplish the result that heretofore needed a plurality of tube units. Furthermore, the characteristics of the gas filled thermionic tube are such that it has high sensitivity to small changes in applied input voltage and relatively large output currents may be drawn from it when ionization takes place and the current once starts to flow from the cathode to the plate. A further advantage of the arrangements of the invention consists in the fact that the sensitive polar receiving relay of former systems may be eliminated because of the increased output available-from the gas filled detector tube. rllhe elimination of the sensitive polar receiving relay will greatly reduce maintenance problems. Other advantages and features of the arrangements of the invention will appear more fully from the detailed description thereof hereinafter given.

'lhe invention may be more fully understoodl from the following description together with the accompanying drawing in the Figures l, 2 and 3 of which the invention is illustrated. Fig. 1 is a circuit diaram embodying a preferred form of the invention. Figs. 2 and 8 are modifications thereof. Similar reference characters have been utilized to denote like parts in all of the gures.

ln Fig. 1 is shown a transmission line L over which signaling currents might be transmitted. For example, a base frequency of 1000 cycles might be utilized for signaling purposes. In order to obtain several distinctive signals this base frequency might be interrupted at different rates such, for example, as 15, 25, and 45 cycles. Bridged across line L would be a. receiving circuit 1 which would be tuned to the base signaling frequency transmitted over line II'when interrupted at the rate of 15, 25, 35 and 45 cycles. Connected through transformer 2 to circuit 1 would be the gas filled thermionic amplifier-detector tube 3. This would have a rid 4, a cathode 5, a heater 6 for the catho e, and a plate electrode 7. The grid bias potential from battery 9 might be chosen so as to be properl related to the normal signal voltages app 'ed to the grid so that current will flow from cathode to plate only when the receiving current approaches the desired input value. Alternating current from source 13 appreciably higher than any of the frequencies used for interrupting the signaling current, that is, considerably er than cycles, is superimposed through transformer 12 on the plate current from battery 11 in order to act as a means of quenching the arc when this is established the input signal. The peak voltage ofV s alternating current would probably be approximately equal to that of the xed direct current voltage. A current limiting resistance 10 is also shown in series with the output circuit of the detector in order to limit the plate current to a desired maximum value.

The action of the gas lled tube 3 in the circuit shown would result in unidirectional pulses of current at the rate of the speeds of interruption of the signaling current, namely 15, 25, 35 and 45 cycles, if these rates of interruption were employed. output transformer 14 is used to deliver effectively alternating current of these frequencies lto thelocal signal receiving circuits. A series resonant circuit of a fairly high degree of selectivity is used in each one of the local signaling branches for each of the low frequencies to be received from the detector. These series resonant circuits are shown as 15, 19, 23 and 27. Since continuous direct current is the final form desired in each of the local signaling relays 17, 21,25 and 29, rectifiers 16, 20, 24 and 28, which might be of the copper oxide variety, are shown included in each of the local signa-ling circuits. The relays 17, 21, 25 and 29 respond selectively to the diiferent signaling currents transmitted over line L. The relays 17, 21, 25 and 29 might control local signaling circuits 18, 22, 26 and 30 as shown.

With a gas illed tube, once the arc has started, it will continue without further applicacation of an input signal, if a suitable posiightive plate voltage is maintained Without superposed alternating current to quench the arc. Accordingly, a gas filled tube in accordance with the arrangements of the invention may be used to provide in effect a locking input signal for a transmitted signal of very short duration, or it may be cmployed to give a flashing signal in response to a continuous transmitted si nal.

In Fig. 2 is shown a mod' vcation of the invention in which a gas filled tube is utilized to provide' a flashing signal in response to a continuous transmitted signal. In Fig. 2 similar reference characters have been utilized to denote like parts with respect to Fig. 1. In Fig. 2 is shown va line L connected by the tuned circuit 1 and transformer 2 to the input of the gas filled amplilier-detector tube 3. The output or plate circuit of the tube includes the Winding of a relay 31. If a continuous signal is transmitted over line L and to the tube 3, the tube will break down and current will flow in the late circuit. This will operate relay 31 w ich will open the plate "circuit and extinguish the arc. This cycle of operations will again be repeated and the relay 31 will be operated intermittently in responseV to a continuous transmitted signal. The relay 31 may operate any desired type of local signaling circuit 32.

In Fig. 3 is shown a further modification of the invention in which a gas filled tube is utilized to provide in effect a locking input signal for a transmitted signal of short duration. Similar reference characters have been utilized in Fig. 3 to denote like parts with respect to, Fig. 1. In Fig. 3 the plate circuit of the gas fiiled tube 3 is completed over the contactscof a jack 34. A signal lamp 33 may also be included in the plate circuit. As has been pointed out with a gas filled tube, once the arc has started in the tube, it will-continue without further application of an input signal. Accordingly, even if the applied signal is of very short duration, the plate circuit of the tube 3 will remain closed when the arc has once started in the tube due to the applied signal, and the lamp 33 will remain lighted after the input signal has closed. The opening of the contacts of jack 34 will extinguish the arc and put out the lamp 33.

While the invention has been disclosed as embodied in certain specific arrangements which are deemed desirable, it is understood that it is capble of embodiment in many and other Widely varied forms Without departing from thespirit of the invention as defined by the appended claims.

What is claimed is:

1. A transmission line over which signaling currents are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signaling frequency, a single gas filled thermionic tube in said signaling circuit operating as an amplifier-detector for said signaling currents, a plurality of individual signal circuits each including rectifying means and direct current signal controlling relays, and means for applying the output of said amplifier-detector tube to said individual signal circuits.

2. A transmission line over which signaling currents of a base frequency interrupted at various rates of frequency are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signaling frequencies, a single gas filled thermionic tube in said signalin circuit operating as an amplifier-detector or said signaling currents, a plurality of individual signal circuits each including rectifying means and direct current signal controlling relays, each of said individual circuits being tuned to different ones of the rates of frequencies at which said base frequency is interrupted, and means for applying the output of said amplifier-detector tube to said individual signal circuits.

3. A transmission line over which signaling currents of a base frequency interrupted at various rates of frequency are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signaling frequencies, a single gas filled thermionic tube in said signalin circuit operating as an amplifier-detector or said signaling currents, a plurality of individual signal circuits each including rectifying means and direct current signal controlling relay, each of said individual circuits being tuned to different ones of the rates of frequencies at which said base frequency is interrupted, means associated with the plate circuit of said tube for periodically quenching the arc created when said tube discharges, and means for applying the output of said amplifier-detector tube to said individual signal circuits.

4. A transmission lineover which signaling currents are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signaling frequency, a single gas illed thermionic tube in said signaling circuit operating as an amplifier-detector for said si naling currents,A signaling means controlled y the output current from said tube, and means associated withthe plate circuit of said tube for quenching the arc created when said tube discharges.

5. A transmission line over which signaling currents are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signalin frequency, a single gas filled thermionic tu naling circuit operatingas an amplifier-detector for said signaling currents, a relay having its winding in series in the plate circuit of said' tube, contacts controlled by said relay for opening said plate circuit, and signaling means controlled by said relay.

6. A transmission line over which signaling currents are transmitted, a signaling circuit connected to said line and tuned to receive currents of said signalin frequency, a single in said sigdevice 

